The application relates to an electromagnetic camshaft adjuster having an armature unit that can be moved relative to a pole core by energising a stationary coil unit and that has an armature plunger as well as a permanent magnet unit, through which the armature unit is held in a resting position in the non-energised condition of the coil unit.
Such an electromagnetic camshaft adjuster is known for example from DE 20 2011 052 220 U1. The permanent magnet unit there has a disc-shaped permanent magnet that is received between a first and second magnetically conductive pole discs. The two pole discs are here welded together with the armature plunger. The end of the armature plunger that protrudes from the housing of the electromagnetic camshaft adjuster engages in a circumferential groove of a cam that can be adjusted on a camshaft. When the coil of the electromagnetic camshaft adjuster is energised, the plunger is forced in the direction of the camshaft and is set back by the camshaft during rotation. This electromagnetic camshaft adjuster has no spring unit.
Another electromagnetic camshaft adjuster is described in EP 2 252 774 B1, which is also placed on the front side of a camshaft of an internal combustion engine and effects an axial movement of the camshaft adjuster as a response to an energisation of the stationary coil unit and by the movement effected thereby of the armature unit or of the associated armature plunger. The yoke unit there is supported in a manner so as to be rotational relative to the coil unit. By contrast, the armature unit with the armature plunger is mounted to be stationary in the rotational yoke and core unit. In this way, the overall armature unit together with the surrounding yoke unit can rotate together with the camshaft.
Finally, also EP 1 421 591 B1 describes an electromagnetic camshaft adjuster. Here, a permanent magnet disc is also provided between two pole discs, which in turn is fixedly connected to the armature unit or the armature plunger. The permanent magnet unit ensures in the resting position, which means when the coil is not energised, that the armature unit is held on the pole core. It is not until the coil is energised with a current that a magnetic field that acts against the field of the permanent magnet discs and the armature unit is repulsed by a spring force supported by the pole core. To this end, a coil spring is provided, the spring force of which is dimensioned to be smaller than the holding force of the permanent magnet disc in the non-energised condition of the coil unit. As soon as the spring force of the coil spring is stronger than an attraction or holding force of the permanent magnet disc, an energisation of the coil with current can be removed and the assembly is held in the extended condition of the armature plunger, without a current having to be supplied to the coil.